The present invention relates to supporting and contacting means for a piezoelectric audio transducer, and particularly to nodal mounting means.
Piezoelectric audio transducers, also known as piezoceramic benders or benders, are enclosed in a housing or holder of some kind and the combination is known as a buzzer. Buzzers presently find use in telephones, electronic games, home appliances, smoke detectors, radar detectors, intrusion alarms, and medical equipment. The transducers are generally mounted in one of three ways: center mount, edge mount, and nodal mount. Nodal mounts are required when maximum sound pressure levels are to be achieved with the minimum transducer drive current since mounting of the transducer at its nodal diameter does not dampen oscillations. Center mounts and edge mounts produce a higher impedance and a lower frequency, and are used where mechanical considerations are more important than electrical, or where it is desirable to force the transducer to vibrate at a frequency lower than its resonant frequency.
Nodal or ring mounts employ a ring of a specific diameter where the natural vibration of the bender exhibits a node, which permits oscillations of greater amplitude than mounting at the outer edge, the center, or any other radius. Several buzzer manufacturers use an adhesive to mount the transducer to a ring in a housing, and the necessary electrical contacts are made by soldering fine wires to the opposite surface on the wafer of piezoelectric ceramic, and the metal surface surrounding the wafer. An alternative to soldered wire is a pressure contact employing resilient metal contacts extending from a housing member which mounts to the housing containing the ring. An example is a buzzer manufactured by BRK Electronics; this employs an adhesive ring mount on the node of the all-metal surface of the transducer, two resilient contacts against the ceramic on the node opposite the ring mount, and a third contact outside the node. An alternative nodal mounting scheme, exemplified by a buzzer manufactured by Molex, Inc., utilizes housing members with rings which bear against the node on opposite surfaces. Electrical contact is achieved by resilient contacts, mounted in one housing member, which bear against the surface having the ceramic. These are not nodal contacts, and thus have a damping effect on the vibration. Even fine wires soldered to the bender tend to dampen oscillations, which decreases efficiency and represents a costly hand operation in buzzer manufacture. It would be most desirable to have a mounting and contacting means in which the mounting and electrical contacts necessary to drive the buzzer could be achieved solely on the nodes for maximum acoustical performance.